Process for preparing 1,4-naphthoquinone compounds



Patented Feb. 12, 1952 PROCESS FOR PREPARING 1,4-NAPHTHO- QUIN ONE COMPOUNDS Harry W. Coover, Jr., and Joseph B. Dickey, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application February 23, 1949, Serial No. 77,976

11 Claims. (Cl. 260-396) a This invention relates to the oxidation of 411,5,- 8,8a-tetrahydro-1,4-naphthoquinone compounds and 5,8-dihydro-lA-naphthoquinone compounds.

It is known to oxidize 4a,5,8,8a-tetrahydro-1,4- naphthoquinone compounds by the use of chromic acid or an alkali metal chromate. The use of such expensive oxidizing agents makes the preparation of 1,4-naphthoquinones by this method expensive.

It is an object of our invention to provide an improved process for oxidizing 4a,5,8,8a-tetrahydro-1,4-naphthoquinone compounds and 5,8- dihydro-1,4-naphthoquinone compounds. Another object of our invention is to provide an improved process for oxidizing a 4a,5,8,8a-tetrahydro-1,4-naphthoquinone compound to a 1,4-naphthoquinone compound. A specific object is to provide an improved process for oxidizing 4a,5,8,8atetrahydro-1,4-naphthoquinone to 1,4-naphthoquinone. A further object is to provide an improved process for oxidizing a 4a,5,8,8a-tetrahydro-1,4-napthoquinone compound to a 5,8-dihydro-lA-napthoquinone compound. A still further object is to provide an improved process for oxidizing 5,8-dihydro-1,4-naphthoquinone compounds to 1,4-napthoquinone compounds.

We have discovered that 4a,5,8,8a-tetrahydro- 1,4-naphthoquinone compounds and 5,8-dihydro- 1,4-naphthoquinone compounds can be readily and inexpensively oxidized to 1,4-naphthoquinone compounds by means of an oxidizing agent such as nitric acid, nitrous acid, the oxides of nitrogen higher than NO and the inorganic nitrites and nitrates which yield nitrous acid and nitric acid, respectively, when treated with a mineral acid such as hydrochloric acid, sulfuric acid and phosphoric acid. Since the '4a,5,8,8a-tetrahydro- 1,4-naphthoquinone compounds are first oxidized to 5,8-dihydro-1,4-naphthoquinone compounds, it follows that our invention also relates to the oxidation of 4a,5,8,8a-tetrahydro-1,4-naphthoquinone compounds to 5,8-dihydro-lA-naphthoquincne compounds.

Inorganic nitrites and nitrates that can be used in carrying out the process of our invention include, for example, sodium nitrite, potassium nitrite, ammonium nitrite, barium nitrite, calcium nitrite, lithium nitrite, strontium nitrite, sodium nitrate, potassium nitrate, ammonium nitrate,

aluminum nitrate, chromium nitrate, cobalt nitrate, copper nitrate, lithium nitrate, magnesium nitrate, manganese nitrate, nickel nitrate, silver nitrate and strontium nitrate.

-The 4a,5,8,8a-tetrahydro-lA-naphthoquincne compounds employed in the process of our invention are known compounds and are readily prepared by the Diels-A-lder reaction. In accordance with this method of preparation, a 1,3-butadiene compound is reacted with a 1,4-benzoquinone compound to form a 4a,5,8,8a-tetrahydro- 1,4-naphthoquinone compound. Thus, 1,3-butadiene reacts with'lA-benzoquinone to form 411,5,- 8,8-a-tetrahydro-1,4-naphthoquinone.

Similarly, 2-methyl-1,3-butadiene reacts with 1,4- benzoquinone to form 7-methyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone.

Also, 2-chloro-1,3-butadiene reacts with 1,4-benzoquinone to form 7-chloro-4a.,5,8,8a-tetrahydro- 1,4-naphthoqui'none.

1,3-butadiene compounds that can be used in the preparation of the 4a,5,8,8a-tetrahydro1,4- naphthoquinone compounds used in the process of our invention include, for example, 1,3-butadiene, Z-methyI-IB-butadiene, 2,3-dimethyl butadiene, 1-methyl-1,3-butadiene (1,3-pentadiene), 1,2-dimethyl-L3-butadiene, 1,3-dimethyl-1,3-butadiene, 1,4dimethyl-1,3-butadiene (dipropenyl), 1-ethyl-1,3-butadiene (1,3-hexadiene), 1-ethyl-4- methyl-1,3-butadiene (2,4-heptadiene), 2-chlor0- 1,3-butadiene, 2-bromo-1,3-butadiene, 2,3-dichloro-L3-butadiene, 2-phenyl-l,3-butadiene and 2- methyli-chloro-1,3-butadiene.

1,4-benzoquinone compounds that can be used in the preparation of the 4a,5,8,8a-tetrahydro- 1,4-naphthoquinone compounds used in the process of our invention include,-for example, 1,4- benzoquinone, 2-bromo-1,4-benzoquinone, Z-chloro-lA-benzoquinone, 2-iodo-1,4-benzoquinone, 2- methyl-lA-benzoquinone, 2-ethy1-1,4-benzoquinone, Z-isopropyl-1,4-benzoquinone, 2-n-amyl-1,- i-benzoquinone, 2 methoxy-1,4-benzoquinone, 2- ethoxy-lA-benzoquinona 2,3-dimethyl-L4-benzoquinone,2,3=-diethy1-1,4-benzoquinone and 2,

dichloro lA-benzoquinone.

Hydro-1,4-naphthoquinone compounds that can be oxidized in accordance with the process of our invention include, for example, 4a,5,8,8atetrahydro-lA-naphthoquinone, 2-methyl-4a,5,- 8,8a-tetrahydro-l,4-naphthoquinone (from 1,3- butadiene and 2-methyl-1,4-benzoquinone), 6,7- dimethyl 4a,5,8,8a tetrahydro 1,4 naphthoquinone (from 2,3-dimethyl-1,3-butadiene and 1,4-benzoquinone), 7-methyl-4a,5,8,8a-tetrahydro-l,4-naphthoquinone, 2-chloro-4a,5,8,8a-tetrahydro-i,4naphthoquinone (from 1,3-butadiene and 2-chloro-1,4-benzoquinone), 2,3-dichloro 4a,5,8,8a tetrahydro 1,4 naphthoquinone, 7 chloro 4a,5,8,8a tetrahydro 1,4- naphthoquinone (from 2-chloro-1A-butadiene and 1,4-benzoquinone), 6,7-dichloro-4a,5,8,8atetrahydro-l,4-naphthoquinone (from 2,3-dichloro-l.3-butadiene and 1,4-benzoquinone), 2 chloro 6,7 dimethyl 4a,5,8,8a tetrahy dro-1,4-naphthoquinone (from 2-chloro-1,4- benzoquinone and 2,3-dimethyl-1,3-butadiene), 2,3 dichloro 6,7 dimethyl 4a,5,8,8a tetrahydro-1,4-naphthoquinone (from 2,3-dichloro- 1,4-benzoquinone and 2,3-dimethyl-1,3-butadiene), 8-methyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (from l-methyl-1,3-butadiene and 1,4-benzoquinone), 8-ethyl-4a,5,8,8a-tetrahydro- 1,4-naphthoquinone (from 1-ethyl-l,3-butadiene and 1,4-benzoquinone), 7-bromo-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (from 2-bromo-l,3- butadiene and 1,4-benzoquinone), 'T-phenyl- 4a,5,8,8a-tetrahydro-l,4-naphthoquinone (from 2-phenyl-1,3-butadiene and 1,4-benzoquinone), 2 bromo 4a,5,8,8a tetrahydro 1,4 naphthoquinone (from 2-bromo-l,4-benz0quinone and 1,3-butadiene), 2-iodo-4a,5,8,8a-tetrahydro- 1,4-naphthoquinone (from 2-iodo-l,4-benzoquinone and 1,3-butadiene), 2-ethyl-4a,5,8,8atetrahydro-1,4-naphthoquinne (from 2-ethyl- 1,4-benzoquinone and 1,3-butadiene), 2-n-amyl- 4a,5,8,8a-tetrahydro-1,4-naphthoquinone (from 2-n-amyl-1,4-benzoquinone and 1,3-butadiene), 2 methoxy 4a,5,8,8a tetrahydro 1,4 naphthoquinone (from 2-methoxy-1,4-benzoquinone and 1,3-butadiene), 2ethoxy-4a,5,8,8a-tetrahydro-l,4-naphthoquinone (from 2-ethoxy-l,4- benzoquinone and 1,3-butadiene), 2,3-dimethyl- 4a,5,8,8a-tetrahydro-1,4-naphthoquinone (from 2,3-dimethyl-1,4-benzoquinone and 1,3-butadiene) and 2,3-diethyl-4a,5,8,8a-tetrahydro-1,4- naphthoquinone (from 2,3-diethyl-L4-benzoquinone and 1,3-butadiene).

So far as we are aware, our process is suitable for the oxidation of any 4a,5,8,8a-tetrahydro- 1,4-naphthoquinone or 5,8-dihydro-L4-naphthoquinone compound. The oxidation reaction consists in the removal of hydrogen from said hydro-1,4-naphthoquinone compounds. Also, as indicated hereinbefore, the hydrogen atoms in the 4a and 8a positions are more readily removable than those in the 5 and 8 positions. Thus, the oxidation of 4a,5,8,8a-tetrahydro-l,4-naphquinone first yields 5,8-dihydro-lA-naphthoquinone and then 1,4-naphthoquinone. Indeed, our experiments indicate that the oxidation reaction is highly selective. To illustrate, if a mixture of 4a,5,8,8a-tetrahydro-1,4-naphthoquinone and 5,8-dihydro-l,4-napthoquinone is being oxidized, the 4a,5,8,8a-tetrahydro-1,4- naphthoquinone will (for all practical purposes) be completely oxidized to 5,8-dihydro-l,4-naphthoquinone before any 5,8-dihydro-1,4-naphthoquinone is oxidized to 1,4-naphth0quinone. That is, very little, 1,4-naphthoquinone is formed while there is any 4a,5,8,8a-tetrahydro- 1,4-naphthoquinone to be oxidized.

When 5,8-dihydro-1,4-naphthoquinone compounds are desired, the reaction is carried out under milder reaction conditions than those employed when 1,4-naphthoquinone compounds are desired. That is, less oxidizing agent and lower reaction temperatures are employed when it is desired to obtain the 5,8-dihydro-L4-naphquinone compounds. Thus, if nitric acid is to be used to oxidize a 4a,5,8,8a-tetrahydro-1,4- naphthoquinone compound to a 5,8-dihydro-L4- naphthoquinone compound preferably only the theoretical amount of nitric acid required should be used. Where 5,8-dihydro-l,4-naphthoquinone compounds are to be prepared, the use of nitrous acid instead of nitric acid is preferred because there is far less danger of carrying the oxidation beyond the desired stage.

From the foregoing, it is apparent that since our process can be used to oxidize 5,8-dihydro-lA-naphthoquinone compounds, it can be used in conjunction with other oxidizing processes, e. g. those which are capable of oxidizing 4a,5,8,8a-tetrahydro-l,4-naphthoquinone compounds to 5,8-dihydro-1,4-naphthoquinone compounds but which are incapable of oxidizing 5,8-dihydro-lA-naphthoquinone compounds to 1,4-naphthoquinone compounds. However, since the present process offers a simple, inexpensive way of oxidizing 4a,5,8,8a-tetrahydro-1,4-naphthoquinones to 1,4-naphthoquinones, there would appear to be little or no occasion for resorting to the two step process just indicated, although such a two step process could be used.

The oxidation reactions of our invention are readily carried out in a lower aliphatic fatty acid medium. Preferably the oxidation is carried out in the presence of acetic acid, although it can be carried out, for example, in the presence of propionic acid or butyric acid. The oxidation can also be carried out on a water suspension of the hydronaphthoquinone compounds, but it has been our experience that a less pure product is obtained than when the reaction is carried out on a solution of the hydronaphthoquinone compound in a lower aliphatic fatty acid. The oxidation will take place at room temperature; however, the best results were obtained by carrying out the oxidation at about C. to C. As shown in the examples, when 1,4-naphthoquinone compounds are desired, the reaction is ordinarily carried out under gentle refluxing conditions. When 5,8-dihydro-lA-naphthoquinone compounds are desired, the reaction is ordinarily carried out at a temperature of about 80 C. It will be understood that the reaction temperatures just given are merely illustrative and not limitative. These temperatures represent temperatures which we have found to be very suitable for carrying out our process, but any suitable temperature can be employed.

When an inorganic nitrate is employed as the oxidizing agent, an acid which will yield nitric acid when reacted with the inorganic nitrate should be present in the reaction mixture. Similarly, when an inorganic nitrate is employed as the oxidizing agent, an acid which will yield nitrous acid when reacted with the inorganic nitrite should be present in the reaction mixture. Suitable acids for this purpose include, for example, acetic acid, hydrochloric acid, propionic acid, butyric acid, sulfuric acid, phosphoric acid, trifiuoroacetic acid and ethane sulfonic acid. Sufficient acid should be present to react with the theoretical amount of oxidizing agent required for the oxidation.

While our process is operative under the conditions set forth herein, we would note that when an inorganic nitrate such as sodium nitrate, for example, is used in conjunction with acetic acid (i. e. no other acid is present) the oxidation re action is slow. If a stronger acid such as hydrochloric acid were used in place of acetic acid, the oxidation reaction would proceed much faster. No reaction appears to take place when one attempts to oxidize a 4a,5,8,8a'tetrahydro-1,4-s naphthoquinone or a 5,8-dihyclro-1A-naphthoquinone compound in water with either an inorganic nitrite or an inorganic nitrate in the ab:

sence of an acid which will yield nitrous acidwhen reacted with the inorganic nitrite or which;v will yield nitric acid when reacted with an in-' organic nitrate. If it is desired to obtain 1,4-naphthoquinone or 5,8-dihydro-lA-naphthoquinone in highly purl 8.1 grams of 4a,5,8,8a-tetrahydro-1,4-naphthoquinone were added to 100 cc. of an aqueous 50% acetic acid solution. 2 cc. of aqueous nitric acid (sp. gr. 1.41) in 2 cc. of water were slowly added to the reaction mixture over a period of to minutes. Then, after stirring for minutes, the reaction mixture was heated togentle reflux, and 5 cc. of aqueous nitric acid (spgr. 1.41) in 5 cc. of water were added over a pee riod of 10 to 15 minutes. Heating, with stirring, was continued for 30 minutes longer, after which the reaction mixture was cooled and poured into 100 cc. of an aqueous 10% sodium chloride solution. 1,4-naphthoquinone precipitated and was recovered by filtration and dried. Following the procedure just described yields of 4.7 to 7.1 grams of 1,4-naphthoquinone melting at 110 C.112 C. equal to 60% to 90% of theory were obtained. Upon crystallization from a solvent such as ethyl alcohol or upon steam distillation substantially pure 1,4-naphthoquinone melting at 122 0,,- 123 C. is obtained as a light yellow crystalline product.

- Example 2 8.1 grams of 5,8-dihydro-1,4-dihydroxynaphthalene, the enolized product of 4a,5,8,8a.-tetrahydro-1,4-naphthoquinone, were suspended in 100 cc. of an aqueous acetic acid solution. 2 cc. of aqueous nitric acid (sp. gr. 1.41) in Z cc. of water were slowly added to the reaction mixture over a period of 10 to 15 minutes. Then. after stirring for 30 minutes, the reaction mixture were heated to gentle reflux, and 5 cc.-of aqueous nitric acid (sp. gr. 1.41) in 5 cc. of water were added over a period of 10 to 15 minutes.

thoquinone melting at 122 C.-123 C. is obtained as a light yellow crystalline product.

Example 3 8.1 grams of 4a,5,8,8a-tetrahydro-1,4-naphthoquinone were added to 100 cc. of an aqueous 50% acetic acid solution. 4 cc. of nitric acid (sp.

7 gr. 1.41) in 4 cc. of water were slowly added, with stirring, to the reaction mixture over a period of 10 to 15 minutes. Following this, the reaction mixture was stirred for 30 minutes and then heated in a water bath to 80 C. for an additional 30 minutes, while stirring. The reaction mixture was cooled and poured into 100 cc. of water. 5,8- dihydro 1,4- naphthoquinone precipitated and was recovered by filtration and dried. The

' yield of product melting at 100 (LE-105 C. was

7.; grams or 93% of theory. Upon crystallization from ethyl alcohol substantially pure 5,8- dihydro-IA-naphthoquinone melting at 109 C.

was obtained as light yellow needles.

Example 4 8.1 grams of 4a,5,8,8a-tetrahydro-1,4-naphthoquinone were added to 50 cc. of water. 2 cc. of nitric acid (sp. gr. 1.41) in 2 cc. of water were slowly added to the stirred reaction mixture over a period of 10 to 15 minutes. Following this, the reaction mixture was stirred for 30 minutes and then heated to gentle reflux and an additional 6 cc. of nitric acid (sp gr. 1.41) in 6 cc. of water were added over a period of 10 to 15 minutes.

Heating, with stirring, was continued for another 30 minutes after which the reaction mixture was cooled and the precipitated 1,4-naphthoquinone was recovered by filtration and dried. A yield of 5.1 grams of 1,4-naphthoquinone melting at 105 C.-l10 C. was obtained. Upon crystallization from a solvent such as ethyl a1 cohol or upon steam distillation substantially pure 1,4-naphthoquinone melting at 122 C.- 123 C. is obtained as a light yellow crystalline product.

The same results are obtained if 8.1 grams of the enol form i. e. 5,8-dihydro-1,4,-dihydroxynaphthalene are used in place of 4a ,5,8a,8-tetrahydro-1,4-naphthoquinone in the foregoing example.

Example 5 8.1 grams of 4a,5,8,8a-tetrahydro-1,4-naphthoquinone were added to 100 cc. of an aqueous 50% acetic acid solution. 7.6 grams of sodium nitrite were added, with stirring, to the reaction mixture over a period of 30 minutes. Then, after stirring for 30 minutes, the reaction mixture was heated in a water bath to C. for an additional 30 minutes, while stirring. The reaction mixture resulting was cooled and poured into cc. of water. lA-naphthoquinone precipitated and was recovered by filtration and dried. The yield of product melting at C.- C. was 5.1 grams. Upon crystallization from ethyl alcohol or by steam distillation, substantially pure 1,4- naphthoquinone' melting at 122 C.-123 C. is obtained as a light yellow crystalline product.

The same results are obtained ii 8.1 grams of the enol form, i. e., 5,8-dihydro-1,4-dihydroxynaphthalene are used in place of 4a,5,5a,8-tetz'ahydro-1,4-naphthoquinone in the foregoing example.

Example 6 8.1 grams of 4a,5,8,8a-tetrahydro-1,4-naphthoquinonewere' added to 100 cc. of an aqueous 50% acetic acid solution. 5.1 grams of nitrogen dioxide were bubbled into the reaction mixture over a period of 15 to 20 minutes, and the reaction mixture was stirred for 30 minutes. Then the reaction mixture was heated to gentle reflux for an additional 30 minutes, while stirring. Following this, the reaction mixture was cooled and the precipitated product, consisting essentially of 1,4-naphthoquinone, was recovered by filtration and dried. 7.1 grams of product melting at 110 C.-112 C. were obtained. Upon crystallization from ethyl alcohol or upon steamdistillation substantially pure 1,4-naphthoquinone melting at 122 C.-123 C. is obtained as a light yellow crystalline product.

Example 7 8.1 grams of 4a,5,8,8a-tetrahydro-1,4-naphthoquinone were added to 100 cc. of an aqueous-50% acetic acid solution. 8.4 grams of nitrogen trioxide (N203) were added to the reaction mixture with stirring over a period of 30 minutes and the reaction mixture was stirred for 30 minutes. Then the reaction mixture was heated to gentle reflux for an additional 30 minutes, while stir- .ring. Following this, the reaction mixture was cooled and the precipitated product, consisting essentially of 1,4-naphthoquinone, was recovered by filtration and dried. About '1 grams of product melting at 110 C.112 C. were obtained. Upon crystallization from ethyl alcohol or upon steam distillation, substantially pure 1,4-naphthoquinone melting at 122 C.123 C. is obtained as a light yellow crystalline product.

Example 8 8.1 grams of 4a,5,8,8a-tetrahydro-1,4-naphthoquinone were added to 100 cc. of an aqueous 50% acetic acid solution. 6.4 grams of nitrogen pentoxide (N205) were added to the reaction mixture with stirring over a period of 30 minutes Example 9 8.1 grams of 4a,5,8,8a-tetrahydro-1,4-naphthoquinone were added to 100 cc. of an aqueous 50% acetic acid solution. 7 cc. of concentrated aqueous hydrochloric acid (sp. gr. 1.14) were added to the reaction mixture and then a concentrated aqueous solution of grams ofsodium nitrate was added slowly over a period of 10 to minutes. The reaction mixture was then stirred for 30 minutes and then heated to gentle reflux for an additional 30 minutes, after which it was cooled. A product consisting essentially of 1,4-naphthoquinone was recovered by filtration and dried. The yield of product melting at 105 C.-1l0 C. was 5 grams. Upon crystalliza-v tion from ethyl alcohol substantially pure,1,4- naphthoquinone melting at 122 C.-123' C. was obtained as a light yellow crystalline product.

Example 10 8.3 grams of "7-methyl-4a,5,8,8a-tetrahydro- 1,4-naphthoquinone were added to 100 cc. of an aqueous-50% acetic acid solution. 4 cc. of nitric acid (sp. gr. 1.41) in 4 cc. of water were slowly added to the reaction mixture over a period of 10 to 15 minutes. Then, after stirring for 30 minutes, the reaction mixture was heated to gentle reflux, and 5 cc. of aqueous nitric acid (sp. gr. 1.41) in 5 cc. of water were added over a period of 10 to 15 minutes. Heating, with stirring, was continued for 30 minutes longer after which the reaction mixture was cooled and poured into cc. of an aqueous 10% sodium chloride solution. About 6 grams of a precipitate consisting essentially of '7 methyl 1,4 naphthoquinone was formed. It was recovered by filtration and dried. Upon crystallization from ethyl alcohol, substantially pure 'l-rriethyl-1,4-naphthoquinone was obtained as a light yellow crystalline product.

Eznample 11 8.5 grams of '7-chloro-4a,5,8,8a-tetrahydro-1,4- naphthoquinone'were oxidized and worked up in accordance with the procedure described in Example 10. A good yield of '7-chloro-1,4-naphthoquinone was obtained as a light yellow crystalline product.

' Example 12 8.5 grams of 2,3-dimethyl-4a,5,8,8a-tetrahydro- 1,4-naphthoquinone (prepared by reacting 2,3- dimethyl-l,4-benzoquinone with 1,3-butadiene) were oxidized and worked up in accordance with the procedure described in Example 10. A good yield of 2,3-dimethyl-1,4-naphthoquinone melting at 126 C.-12'7 C. was obtained as a light yellow crystalline product.

By the use of 8.5 grams of 6,7-dimethyl- 4a,5,8,8a-tetrahydro-1,4-naphthoquinone in place of 2,3-dimethyl-4a,5,8,8a-tetrahydro 1,4 naphthoquinone in the foregoing example, 6,7-dlmethyl-1,4-naphthoquinone melting at 117 C. 119 C. is obtained as a light yellow crystalline product. 4

Example 13 Example 15 8 grams of 5,8-dihydro-1,4-naphthoquinone were added to 100 cc. of an aqueous 50% acetic acidsolution. 4 cc. of nitric acid (sp. gr. 1.41) in 4cc. of water were gradually added to the reaction mixture and then the reaction mixture was refluxed gently for 30 minutes. Following this. the reaction mixture was cooled and Poured into 100 cc." of water and the 1,4-naphthoquinone which precipitated was recovered by filtration and dried. A yield of '7 grams was obtained. Upon crystallization from ethyl alcohol the 1,4-naphthoquinone which is obtained as a light yellow crystalline product melts at 122 C.-l23 C.

Example 16 9.4 grams of 4a,5,8 ,8a-tetrahydro-6,7-dirnethyl- 1,4-naphthoquinone were added to 100 cc. of an aqueous 50% acetic acid solution. 8 cc. of nitric acid were slowly added to the stirred reaction mixture over a period of 30 minutes. The reaction mixture was then heated to gentle reflux for a period of 30 minutes. Following this, the reaction mixture was cooled and poured into 100 cc. of water and the 6,7-dimethyl-1,4-naphthoquinone which precipitated as a yellow product was recovered by filtration and dried. A yield of 8 grams was obtained.

As illustrated in the foregoing examples, the hydronaphthoquinone compounds of our invention can be used in their naphthoquinone or enol form. Accordingly, it is to be understood that in the claims which follow while the compounds undergoing oxidation are referred to as hydronaphthoquinone compounds, the enol form of these compounds is also intended.

We claim:

1. A process for oxidizing a compound selected from the group consisting of 4a,5,8,8a-tetrahydro-1,4-naphthoquinone compounds and 5,8 dihydro-1,4-naphthoquinone compounds which comprises reacting said compound with an oxidizing agent selected from the group consisting of dilute nitric acid, nitrous acid and the oxides of nitrogen higher than NO and wherein said oxidation process consists in the removal of hydro hydrogen from the 4a,5,8 or 8a-positions of the aforesaid 1,4-naphthoquinone compounds.

2. A process for oxidizing a 4a,5,8,8a-tetrahydro-1,4-naphthoquinone compound which comprises causing a 4a,5,8,8a-tetrahydro-1,4-naphthoquinone compound to react with dilute nitric acid to obtain a compound selected from the group consisting of a, 5,8-dihydro-1,4-naphthoquinone compound and a 1,4-naphthoquinone compound.

3. The process which comprises reacting a 4a,5,8,8a-tetrahydro-1,4-naphthoquinone compound with dilute nitric acid to obtain a 1,4- naphthoquinone compound. I

4. The process which comprises reacting a 4a,5,8,8u.-tetrahydro-1,4-naphthoquinone compound with nitric acid in the presence of a sub stantial amount of lower aliphatic fatty acid to obtain a 1,4-naphthoquinone compound.

5. The process which comprises reacting 4a,5,8,8a-tetrahydro-1,4-naphthoquinone with nitric acid in the presence of a substantial amount of acetic acid to obtain 1,4-naphthoquinone.

6. A process for oxidizing a 4a,5,8,8a-tetrahydro-1,4-naphthoquinone compound which comprises causing a 4a,'5,8,8a-tetrahydro-1,4- naphthoquinone compound to react with an oxide of nitrogen higher than NO to obtain a compound selected from the group consisting of a 5,8-dihydro-1,4-naphthoquinone compound and a 1,4-naphthoquinone compound.

7. The process which comprises reacting a 4a,5,8,8a-tetrahydro-1,4-naphthoquinone compound with an oxide of nitrogen higher than NO to obtain a 1,4-naphthoquinone compound.

8. The process which comprises reacting a 4a,5,8,8a-tetrahydro-1,4-naphthoquinone compound with an oxide of nitrogen higher than NO in the presence of a lower aliphatic fatty acid to obtain a 1,4-naphthoquinone compound.

9. The process which comprises reacting 4a,5,8,8a-tetrahydro-1,4-naphthoquinone with an oxide of nitrogen higher than N0 in the presence of acetic acid to obtain 1,4-naphthoquinone.

10. A process for oxidizing 4a,5,8,8a-tetrahydro-lA-naphthoquinone to 5,8-dihydro-1,4-naphthoquinone which comprises causing 4a,5,8,8atetrahydro-1,4-naphthoquinone to react with approximately the theoretical amount of dilute nitric acid required to oxidize 4a,5,8,8a-tetrahydro- 1,4-naphthoquinone to 5,8-dihydro-L4-naphthoquinone and recovering the 5,8-dihydro-L4- naphthoquinone thus formed.

11. A process for oxidizing 4a,5,8,8a-tetrahydro-lA-naphthoquinone to 5,8-dihydro-L4- naphthoquinone which comprises causing 4a,5,8,8a-tetrahydro-1,4-naphthoquinone to react with nitrous acid to form 5,8-dihydro-L4-naphthoquinone and recovering the 5,8-dihydro-L4- naphthoquinone thus formed.

HARRY W. COOVER, JR. JOSEPH B. DICKEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,891,168 Luettringhaus Dec. 13, 1932 1,967,862 Carothers July 24, 1934 

1. A PROCESS FOR OXIDIZING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF 4A,5,8,8A-TETRAHYDRO-1,4-NAPHTHOQUINONE COMPOUNDS AND 5,8DIHYDRO-1,4-NAPHTHOQUINONE COMPOUNDS AND WHICH COMPRISES REACTING SAID COMPOUND WITH AN OXIDIZING AGENT SELECTED FROM THE GROUP CONSISTING OF DILITE NITRIC ACID, NITROUS ACID AND THE OXIDES OF NITROGEN HIGHER THAN NO AND WHEREIN SAID OXIDATION PROCESS CONSISTS IN THE REMOVAL OF HYDRO HYDROGEN FROM THE 4A,5,8 OR 8A-POSITIONIS OF THE AFORESAID 1,4-NAPHTHOQUINONE COMPOUNDS. 